The present invention relates to a radio-controlled device that controls a mobile object. Particularly, the present invention relates to a radio-controlled device suitable for use with radio-controlled cars requiring instantaneous response characteristics.
A radio-control (R/C) technique is used to control mobile objects as equipment subject to control, such as small model cars, model aircraft, and model ships. Generally, plural sets of control information are used to operate the control object. For example, in order to manipulate a model car, three kinds of control information, related to directional (steering) control, forward movement (accelerating), and stopping (braking), are created and used as control signals.
FIG. 8 shows the outline of the radio-controlled device, a transmitter 50 consists of a controller 51, an encoder 52, a high-frequency section 53, and an antenna 54. The controller 51 has levers or joysticks 51a each for manipulating a mobile object, or an object subject to control, for example, a model car (hereinafter, referred to as a radio-controlled car) 55, and various setting switches. While the switch 51a is rotated with fingers, the volume (potentiometer) 51b connected to the joystick 51a rotates together. Thus, control signals proportional to rotational angles of the joystick are created via the voltage indicated by the volume 51b. The encoder 52 performs a PPM conversion and converts various signals output from the controller 51 into a chain of pulses serially-arranged concluded in a predetermined frame period. While a radio-controlled car is being operated, the high-frequency section 53 (transmission section) receives the chain of pulses and the antenna 54 radiates AM- or FM-modulated carriers at all times. In a contest, a manipulator, or a player, carries a transmitter while operating a joystick 51a to move a radio-controlled model car 55 at a remote place.
FIG. 9 is a block diagram illustrating a receiver 60 mounted on the radio-controlled model car 55. The antenna 61 receives radio waves transmitted by the transmitter shown in FIG. 8. The decoder 65 decodes the radio waves into a PPM signal via the tuner 62, the converter 63 connected to the local-oscillator 64, and the IF amplifier/FM detection circuit 67. The decoder signal output is distributed to each servomechanism. Each servomotor is driven by each signal to control the direction and speed of the radio-controlled model car. Normally, in order to indicate the current rotational position of the output shaft of a servomechanism, a potentiometer is connected to the output shaft thereof. In control, the rotational angle of the output shaft of the servomechanism is substantially proportional to the operation angle of the joystick.
FIG. 10 is an example of a format of control signals created by the encoder 52 in the transmitter 50. Referring to FIG. 10, the horizontal axis represents a time axis with time lapsing from left to right. The PPM converted control signals are respectively shown as signals T1 to T3 arranged in the order of CH1 to CH3. The duration of each signal corresponds to a position (angle) of a joystick 51a. One shot pulse S is created at the beginning of a signal corresponding to each channel. The time period (time width) between the start time of one-shot pulse S and the start time of the next one-shot pulse S corresponds to T1, T2, or T3.
Symbol S1, S2, S3, or SR is attached to one-shot pulse S. The time period between one-shot pulse S1 showing the beginning of the channel (CH1) and the next one-shot pulse S1 forms one frame. The frame is created sequentially and transmitted seamlessly. Each of signals T1 and T3 in each channel has a minimum time width of 900 μs and a maximum time width of 2100 μs. Each of the signals T1 to T3 has the time period proportional to an operation amount of the corresponding joystick 51a. Thus, the total of the signal time periods in the three channels ranges from a minimum value of 2700 μs to a maximum value of 6300 μs.
One-shot pulse SR formed at the end of the channel 3 (CH3) is used as a reset pulse R. Referring to FIG. 10, symbols S1, S2, S3, or SR are distinctively attached to one-shot pulse S. All one-shot pulses S have the same pulse width (a) and the same shape. Even when the receiver side receives a sole pulse, whether or not what symbol it belongs to cannot be specified. In order to specify one-shot pulse S1 and to decide the signal T1, non-signal time period between one-shot pulse S1 from the rise time of the reset pulse SR, or a reset signal, and one-shot pulse S1 showing the beginning of the next channel is at least 5 ms (5000 μs), different from a maximum interval of 2100 μs of other pulses.
When one-shot pulse S cannot be received because of, for example, noises, the receiver side cannot specify whether or not what channel it belongs to. In such a case, a pulse interval is measured and a reset signal set to a longer time than 5 ms is decided. Thus, it is assumed that the one-shot pulse S to be received next is the one-shot pulse S1. It is assumed that a new frame begins from the one-shot pulse S1. Thus, one-shot pulses S1, S2 and S3 at the beginnings of respective channels serially-arranged channels are specified.
In the block diagram shown in FIG. 9, the (PPM) decoder circuit 65 extracts reset data through an analog process. As shown with the column RES of FIG. 10, the RC circuit in the decoder 65 is charged via the inverter 66 for the duration only of the signals T1 to T3 and then is discharged with the next one-shot pulse S. Because the duration of the signal T1 to T3 is short, the charging voltage does not exceed the threshold value shown with the broken lines. However, because the reset signal SR has a sufficient long period of time, the charging voltage exceeds the threshold value and is recognized as a rest signal.
For the conventional servomotor, the frame length must be fixed to stabilize the operation. Even if all channel pulses are changed to a maximum value, the reset pulse must be set to a larger value. For that reason, the more the number of channels is increased, the more the frame length is prolonged. In order to obtain stability of the servomechanism, it is desirable to provide a margin time period per frame and to maintain the constant duration of each frame. Hence, the length of one frame is fixed to, for example, 14 ms. The non-signal duration of the reset signal is changed to deal with a variation of the total of the signal time widths of respective channels. Thus, making the reset signal longer than other signals and maintaining the time period of one frame to a constant value are required to cope with the mixing of noise and with stable drive operation of the servomechanism.
In the above system, information on position of a joystick is captured as a voltage indicated by a volume connected directly to the joystick at the points of the beginnings of one-shot pulses S1 to S3. The signals corresponding to the duration T1 to T3 are supplied as the pulses (hatched) to respective servomechanisms, once for one frame. Consequently, the travel angle of the joystick after an end of capture is not transmitted as stick travel information until one-shot pulses S1 to S3 corresponding to the next frame begin. That is, a maximum time of 14 ms corresponding to the length of one frame becomes non-operation area where the servomechanism does not follow the movement of the joystick. To the extent of non-operation area, a time difference occurs between movement of the joystick and the movement of a servomechanism. This results in poor control responsivity.
Servomechanisms used for general radio-controlled devices have a maximum operation angle of 60° to one side. In the operational speed of servomechanisms for model cars, it takes 100 to 150 ms to rotate the output shaft by 60°. That is, even when the signal having a time width corresponding to the maximum operation angle, the output shaft of each servomechanism is completely moved after a lapse of the time period corresponding to several frames. Accordingly, when the servomechanism operates nearly to the fullest extent, it is difficult that the conventional radio-controlled device senses non-operation area, which has 10 ms corresponding to less than 10% of the fullest extent. Thus, that system will not occur any problem. Moreover, with a small operation angle or the case where the servomechanism completely operates within the time period of one frame, the player is not often conscious of the delay of 10 ms in tracking, as a whole.
However, in the case of the radio-controlled model car contest for contending for, particularly, car speed, top-level players can often repeat minute displacements of the joystick at very high rate at the corner of a racing circuit for competition. Because of their natural abilities or skills, they can finger the joystick at a rate of 10 ms or less. It is considered that they have an unusual ability detectable a minute time. The time period of several tens ms of the non-operational area of the servomechanism corresponds to a change of several tens cm in position, when the speed of the current radio-controlled model car is converted into distance. During the change in position, the radio-controlled model car does not respond to any delicate, repeat operation of the joystick. Top players have been dissatisfied with the fact that the response characteristic of the current radio-controlled device, to which the servomechanism cannot track to the joystick operation by fingers, does not fully draw their steering skills. In order to gain ascendancy in competition, there have been strong demands for improved responsivity of the servomechanism that can follow quick finger movement.
A limited number of players are ranked among the tops. However, radio controlled model cars in which good results have been proven by the first-ranking players will show outstanding advertisement effects. Hence, because the superior-performance-proven model cars are expected to lead to a large volume of sales, improving the response characteristics of a servomechanism is a significant challenge to the business strategy.
Recently, a digital servomechanisms in an autonomous control system, each which uses a servomotor stably operating without fixing the frame length, have appeared on the market. The digital servomechanism does not require the frame length required in the conventional art but operates stably with the short frame length. That is, the use of the digital servomechanism allows the time period of one frame to be reduced in the driving of the servomechanism.